The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, a diesel engine performs a swirl control on intake air by mounting a swirl control valve (SCV) in a passage of intake air flowing into a combustion chamber in order to more completely combust the intake air.
According to the swirl control, swirl is generated when intake air passes the SCV, and intake air, in which the swirl is generated, is supplied to the combustion chamber and well mixed with diesel fuel, so that it is possible to improve combustion efficiency, reduce exhaust gas, reduce particulate matters (PM), and the like.
A variable control method through a motor is mainly used as the method of controlling an operation of the SCV. An opening degree of the SCV may be freely controlled according to an engine operation region through a link unit connected with the motor.
For example, it is necessary to precisely control opening/closing of the SCV, such as closing the SCV in order to reduce exhaust gas in a middle/low load operation region of the engine, and opening the SCV so as to supply the large amount of intake air to the combustion chamber and improve output performance of the engine in a high load region.
However, the SCV of the diesel engine is not a component which is capable of always using a desired maximum current, because a coil temperature of the motor increases according to a use current and a use time of the motor of the SCV, and a surrounding temperature, and a coil resistant temperature is 180° C.
According to a characteristic of the SCV, a maximum motor duty (100%) may be used for three seconds, but it is recommended to use a limited, actual use, motor duty in consideration of preventing an excessive increase in a coil temperature.
TABLE 1SCV motor(limit 180° C.)itemcurrent(A)−40° C.RT130° C.10.5stable atabout 151° C.21.04.6 minutesto 180° C.31.561 secondsto 180° C.42.021 secondsto 180° C.52.511.5 secondsto 180° C.63.075 seconds41 seconds6 secondsto 180° C.to 180° C.to 180° C.
Table 1 is an experimental result representing our discoveries, and shows a time taken for increasing a coil temperature to 180° C. when a motor for operating the SCV is driven with a predetermined current, and it can be seen that when a current is continuously applied with 1.0 A, a use time limit of the SCV needs to be 4.6 minutes, and as a driving current is increased, a use permitted time is decreased.
TABLE 2SCV motor(limit 180° C.)itemcurrent(A)chamber temperature 130° C.10.5stable at 151.1° C.20.6stable at 161° C.30.7stable at 173.6° C.40.8>180° C.
Table 2 is an experimental result representing our discoveries, and was obtained by measuring a driving current limit value according to a temperature for preventing the SCV from being damaged, and it can be seen that when the motor is driven with 0.7 A, the motor is stable at 173.6° C., and when a driving current is increased to 0.8 A, the chamber temperature exceeds 180° C., which is a coil temperature, at which the SCV is resistible, and it can be seen through the experiment that in order to prevent the SCV from being damaged, a driving current of the motor of the SCV limited by an electronic control unit (ECU) controlling an operation of the SCV is 0.7 A.
The ECU commands a motor duty to the motor for operating the SCV through a pulse width modulation (PWM) communication, and our discoveries from an experimental result for a motor duty limit value of the ECU for limiting the driving current to 0.7 A is represented in Table 3 below.
TABLE 3SCV motor (limit 180° C.)Motor duty5%10%15%20%25%30%35%40%1Room temperature0.1790.3100.4620.6410.7840.9511.1231.261130° C.0.1700.3200.4410.5510.6670.8050.9281.0342Room temperature0.1960.3270.4910.6690.8170.9771.1461.303High temperature0.1770.2980.4640.5390.7680.8000.9341.0693Room temperature0.2010.3270.4870.6490.8080.9691.1201.274High temperature0.1640.2770.4440.5310.6470.780.0.9071.0334Room temperature0.1500.2870.4460.6220.8170.9341.0991.262High temperature0.1460.2900.3870.5220.6320.7670.9501.1735Room temperature0.1170.2500.4670.5900.7291.0281.2311.397High temperature0.1440.2600.3800.5220.6490.7760.8971.020
We have discovered that, and as can be seen in Table 3, when the ECU applies the motor duty of 25%, a current output value for the motor is different according to a surrounding temperature (for example, a motor coil temperature) of the SCV.
For example, when the ECU applies the motor duty of 25%, a current output value is 0.784 A at a room temperature, but the current output value is decreased to 0.667 A at a high and bad temperature condition of 130° C.
That is, it can be seen that when a temperature is increased, an output current with respect to the same duty is decreased, and a duty limit value of the ECU needs to be further decreased at a high temperature.
Accordingly, the ECU needs to consider a bad condition in setting a motor duty limit value of the SCV, so that finally, in order to limit the output current to 0.7 A, the duty needs to be limited to 25%.
However, when a motor-providing company limits the motor duty to 25% in order to protect the motor of the SCV, there is a problem in that engine developers cannot calibrate a motor duty by a desired level.
Realistically, when a motor duty limit value of 25% is applied to an actual vehicle, there is a problem in that an operation response of the SCV is late due to a lack of proportional integral and derivative (PID) gain according to a lack of duty, and a side effect, such as an error generation of a large deviation between a target duty and an actual duty, is generated.